ES2357763T3 - DEMETALIZATION PROCEDURE OF OPTICAL MEDIA. - Google Patents

Abstract

A process for removing the coating and any metals from polymeric substrates such as compact discs (CDs) and digital video discs (DVDs) by applying high shear conditions to fluidized particulates of the polymeric substrate optionally in the presence of an accelerant.

Description

FIELD OF THE INVENTION

The invention relates to the removal of coatings (based on metals, organic and / or inorganic compounds) from polymeric substrates. More particularly, the present invention relates to a method of demetalization of optical media. Most particularly, the present invention relates to demetalizing optical media with high shear in the presence of an aqueous medium. In a particularly preferred embodiment, the present invention relates to demetalizing optical media in the presence of an organic acid under high shear conditions. The present invention also has application in the removal of lacquers and / or metals from a variety of other products, including, but not limited to, headlight lenses or automobile trim components.

BACKGROUND OF THE INVENTION

Polymeric substrates are often used in a variety of applications in which a coating is applied to protect the underlying polymeric substrate while maintaining optical clarity and / or improving impact resistance. It is also known that polymeric substrates are coated for decorative purposes, such as paints, and to impart a variety of other functional properties to the substrate. For example, polycarbonate sheets are often immersed in a solution to form silicone hard layers, dried and then cured by known methods. Additional protective coatings commonly used on polycarbonate articles are acrylic hard layers and hard layers on formaldehyde-melamine resins. It is known that other polymeric materials in addition to polycarbonates are similarly coated, such as a sheet of polymethacrylate initially treated with a thermosetting acrylic primer followed by the application of a hard silicone layer.

Polycarbonates used for optical media, such as compact discs (CDs) and / or digital video discs (DVDs) present a particular problem. The CDs are metallized with aluminum and then superficially sealed with lacquers that can optionally be printed. The halves of the DVDs are metallized with gold and aluminum, respectively. An adhesive is then used to bond the two halves together. Next, the DVD is optionally coated with an acrylic material or a lacquer and optionally an impression is applied thereon.

End users and manufacturers of polymeric materials such as those found in the polycarbonate industry have faced increasing environmental problems due to the proliferation of CDs and DVDs that are becoming increasingly common in daily life. The use of metals on the surfaces of these articles gives rise to significant environmental problems with their disposal. The lack of adequate means to demetalize surfaces in an ecological way has made CDs and DVDs difficult to recycle. Thus, the spill has typically become the method of disposal chosen, which has significant environmental problems.

Current procedures for the demetalization of optical media involve the use of a caustic solution such as sodium hydroxide. See, for example, Eddy Helenek et al., U.S. Patent No. 5,817,183; Nee, U.S. Patent No. 5,306,349, and Franci, U.S. Patent No. 5,464,877. Although these procedures have been shown to have some effect on demetalization, the caustic solution can cause appreciable damage to the polycarbonate polymer substrate by decreasing the molecular weight of the polycarbonate. There are additional environmental and OSHA consequences associated with the use of caustic solutions on polycarbonates. One of these consequences is the possible generation of bisphenol A monomer in effluent process streams.

Mention is also made of Fennhoff et al., U.S. Patent No. 5,151,452, which disclosed using acidic media at reflux temperature and low shear conditions. Although this procedure would have some beneficial effect to demetalize CDs, the lack of recognition of the need for high shear conditions to effect gold demetalization on DVD makes this procedure ineffective in many applications. On the other hand, the lacquer removal procedure of Fennhoff et al. ’452 clearly depends on the chemical interaction between the acids and the materials sought and thus does not even remotely suggest the removal of lacquer / metal by the high shear mechanical methods of the present invention.

Thus, it would represent a remarkable advance in the state of the specialty that a relatively environmentally benign process for removing coatings (optionally including metals) from a variety of polymeric residual materials surface treated with metals would be developed.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides an improved coating removal process that processes the polymeric substrate by peeling off the polymeric substrate, intimately mixing the polymeric flakes under fluidized and relatively high shear conditions in order to effect the removal of the coating and any metal or metals, adhesive and coating layers of the polymeric substrate, thereby creating a clean polymer scale not damaged for recycling and allowing recovery of metals removed from the effluent through filtration or other separation or extraction techniques known to the experts normal in the specialty. Optionally, the shear can take place in the presence of a chemical accelerator such as one or more esters of carboxylic acid, carboxylic acids or mixtures thereof.

In the case of DVDs, the present invention also surprisingly provides an effective method for recovering the valuable gold content of DVDs. Accordingly, the process of the present invention can also be performed in a closed circuit configuration to reduce environmental effects, in which the release of fumes and effluent is kept relatively low and any active chemicals are preserved.

In one embodiment of the present invention, there is provided a method for cleaning a polymeric substrate having a coating thereon, the process comprising the steps of: (a) mechanically peeling or granulating the polymeric substrate into relatively small particles; (b) providing the polymeric substrate particles to a mechanical shear apparatus; (c) fluidize the polymeric substrate particles; (d) shear the fluidized particles to shear at a relatively high shear rate equivalent to a blade speed of more than 800 rpm and a circumferential blade speed of at least 10 m / s, optionally in the presence of an accelerator selected from the group consisting of carboxylic acids, carboxylic acid esters and mixtures thereof, to clean the polymeric substrate; and (e) recovering the cleaned polymeric particles, in which the fluidization medium comprises water, is free of caustic agents and the solids content in the fluidization medium ranges from 50 to 60% by weight. In especially preferred embodiments of the present invention, the coating on the polymer particles includes a metal substance and the process of the present invention substantially completely demetalizes the polymer particles, that is, up to 20 ppm by weight of metal or less.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention provides a method for removing a coating from a coated polymeric substrate, the process comprising the steps of: (a) fragmenting the polymeric substrate into relatively small polymeric substrate particles; (b) providing the polymeric substrate particles to a mechanical shear apparatus; (c) fluidize the polymeric substrate particles; (d) shearing the particles at a relatively high shear rate, optionally in the presence of an accelerator selected from the group consisting of carboxylic acids, carboxylic acid esters and mixtures thereof, to remove the coating of the polymeric substrate; and (e) recover the cleaned polymer particles.

Although polycarbonate substrates such as compact discs are used illustratively throughout the present specification, it should be understood that the process of the present invention applies to a wide variety of polymeric substrates that have been surface coated, optionally when the surface coating also It includes metals. For example, the method of the present invention can also be used to clean aromatic polyester carbonates that accumulate in the production of lenses for glasses or other optical applications, or reflectors of lamps or headlights.

First, the polymeric substrate is reduced in particles, fragments, scales, granules, chips and the like by means well known to those of ordinary skill in the art. For example, the polymeric material can be cut or chopped, crumbled, granulated, flaked, crushed or crushed into relatively small individual macroparticles. Flaking helps improve the flow characteristics of the suspension during shear. The macroparticles are not required to have a regular size and conformation, and in a preferred embodiment the macroparticles are irregularly shaped and comprise macroparticles ranging in size from about 2 to about 20 millimeters, preferably from about 4 to about 10 millimeters, in The longest address. The macroparticles can consist of DVD, CD or other plastic substrates, alone or mixed together.

Next, the macroparticles are supplied to a mechanical shear apparatus and fluidized. The effects of coating removal and / or demetalization of fluidized macroparticles are significantly improved through the use of high intensity shear mixing, which promotes the turbulence of the suspension and increases the particle-particle interaction and / or the particle- interactions. mixing blade and / or the interactions between the particles and any solid parts (walls, accessories and the like) in the shear container. Excellent results can be reproduced in almost any industrial equipment that facilitates high shear mixing.

For example, an industrial high-speed rotating blade mixer, with blade speeds of more than 800 rpm, more preferably more than 100 rpm and most preferably more than 1250 rpm, would be suitable for use in the practice of the present invention. . Also, the circumferential speed of the blades in the mixers should be relatively high, of the order of at least 10 m / s, preferably at least 15 m / s, and most preferably at least 18 m / s. The mill can also be designed to improve shear interaction by using a suitable propeller design, that is, number, geometry, diameter and position; proper design of the container, that is, to reduce time in dead zones; and other design factors, that is, the presence and design of a scanning cage. Addition mills without friction means are suitable for use as a mechanical shear apparatus according to the invention.

The fluidization means of the macroparticles in the mechanical shear apparatus may be air, such as that from a fan, water or other liquid systems. Water is especially preferred.

In the mechanical shear apparatus, polymer substrate chips can also be contacted with an accelerator. Accelerators useful in the practice of the present invention comprise carboxylic acids, carboxylic acid esters and mixtures thereof. Although excellent results are obtained using water alone, that is without an accelerator, the use of accelerators such as carboxylic acids or aqueous carboxylic acid esters can reduce the shear time and / or the shear temperature required to effect deestatification and / or demetalization . In those cases, the concentration of acid or ester is preferably in the range of about 0.1 to 20 weight percent, more preferably about 0.1 to about 10 weight percent, and most preferably about 0, 25 to about 1 percent by weight.

Other materials may also be added with the accelerator, such as conventional surfactants, soaps and salts, when it is desired to help clean the polymeric substrate particles.

The carboxylic acids useful in the practice of the present invention include all known to persons of ordinary skill in the art. Acetic acid is especially preferred. It is believed that acetic acid also acts to embrittle the adhesive on the DVD scale thereby improving the efficiency of the high shear process, although the inventors do not wish to limit themselves to any particular theory. In addition, it is also believed that acetic acid prevents the metal or coating macroparticles from being redeposited on the polymer flaky substrate, perhaps due to the properties of charge dissipation or surfactants, although again the inventors do not wish to limit themselves to any particular theory. Also, any of the known carboxylic acid esters may be employed in the practice of the present invention, although lactates, such as ethyl lactate, are preferred.

When loading the thermoplastic substrate chips and the accelerator to the mechanical shear apparatus, the solids content in the fluidizing medium must be as high as practicable, such as approximately 60%, to achieve the best results, provided that keep the mixing of the chips helped by fluid. In preferred embodiments, the solids content ranges from about 20 to about 60%. Higher solids contents are possible depending on the equipment, but difficulties in handling (pumping) materials and mixing behavior can lead to inefficiencies of the procedure.

The temperature of the mixture in the mechanical shear apparatus must be kept below the reflux temperature for the particular conditions employed during the shear process. A shear temperature in the range of about 50 ° to about 95 ° C, more preferably from about 60 ° to about 95 ° C, and most preferably from about 80 to about 95 ° C is preferred. Generally, no heat needs to be added since high shear typically generates enough heat. In fact, in some cases a cooling jacket may be required on the mixing apparatus to prevent the temperature from rising too high. Thus, the shear portion of the process of the present invention can be started at room temperature and a desired high shear temperature can be achieved only by friction. Alternatively, it is contemplated to preheat the mixture in the shear apparatus to a desired preheat temperature, such as from about 50 to about 70 ° C, or even to the desired shear temperature.

The fluidized macroparticles are subjected to shear under these relatively high shear conditions until removal and optionally demetalization is complete, typically in the range of about 0.5 to about 3.0 hours, preferably about 1.0 to 2 hours . The shear time depends on the amount and type of accelerator (if used), the solids content, the shear rate, the temperature and the size and thickness of the scales.

It has been pointed out by the inventors that the combined effect of solids content and shear rate exhibits synergy since the combined effect of these two parameters is greater than the additive effect of each parameter individually. In tests of various optical media with respect to the metal content before and after processing according to the present invention, the aluminum content has been consistently reduced from 90-100 ppm by weight to approximately 6-9 ppm by weight. Similarly, gold has been consistently reduced from more than 150 ppm by weight to less than about 20 ppm by weight.

After the removal of the coating and the optional demetalization is completed, the cleaned polymer substrate is recovered by washing, filtration and / or drying procedures in conventional apparatus that are

5 well known to experts in the field. The recovered thermoplastic particles are cleaned of metals, adhesives, pigments, dyes and other coatings in an undamaged state, suitable for recycling and reuse in molding operations. In the washing phases, it is contemplated that the washing may include a washing additive such as organic acids (including acetic acid) or other conventional surface agents (soaps) in order to improve the cleanliness of the CD and / or DVD scale , when necessary or desired.

The effluent from the filtration stage can be further treated to recover metals through filtration or other separation or extraction techniques known to those of ordinary skill in the art. In the case of DVDs, the present invention surprisingly also provides an effective method for recovering the valuable gold content of DVDs.

It is also contemplated by the present invention that the process of the present invention can be performed in a closed circuit configuration to reduce environmental effects, in which the release of fumes and effluent is kept low and any active chemicals are preserved. In this type of embodiment, the filtration effluent is cleaned of metals and other contaminants by filtration and other separation procedures known to those skilled in the art and recycled to the shear stage for reuse as an accelerator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples are provided for illustrative purposes and should not be considered at all to limit the scope of the claims.

Examples

25 EXAMPLE 1

A suspension of compact discs in 60% flakes (2220 g) and a 40% solution of 20% acetic acid (1184 g of water / 296 g of acetic acid) were placed in a friction mill that operated at 1025 rpm at room temperature without friction. After 2 hours, the mill was heated to 53 ° C. After two hours there was 100% de-stratification and demetalization.

EXAMPLE 2

A suspension of digital video disc in 60% scales (2220 g) and a 40% solution of 20% acetic acid (1184 g of water / 296 g of acetic acid) were placed in a friction mill that operated at 1025 rpm at room temperature without friction. After 2 hours, the mill was heated to 58 ° C and the polycarbonate of the DVDs was 100% demetallized and seemed very clean although there was almost residual gold

35 imperceptible.

EXAMPLE 3

A suspension of compact discs in 60% flakes (2220 g) and a 40% solution of 20% acetic acid (1184 g of water / 296 g of acetic acid) were placed in a friction mill that operated at 1025 rpm at room temperature without friction. In addition, 1% (14.8 g) of NaCl solution was added. At 30 minutes there was less than 50% de-stratification. After 60 minutes there was 80-90% de-stratification. After 90 minutes there was 95-99% deestratification. After 2 hours the mill was heated to 53 ° C and there was 100% de-stratification and demetalization.

EXAMPLE 4

A suspension of compact discs in 60% flakes (2220 g) and a 40% solution of 20% acetic acid

45 (1184 g of water / 296 g of acetic acid) were placed in a friction mill that operated at 1025 rpm at room temperature without friction. In addition, 3% (44.4 g) of NaCl solution was added. At 30 minutes there was less than 50% de-stratification. After 60 minutes there was 80-90% de-stratification. After 90 minutes there was 95-99% deestratification. After 2 hours the mill was heated to 53 ° C and there was 100% de-stratification and demetalization. The product seemed slightly lighter than in the 1% NaCl experiment (Example 3) at 2 hours.

EXAMPLE 5

A suspension of compact discs in 60% flakes (2220 g) and a 40% solution of 10% acetic acid (1332 g of water / 148 g of acetic acid) were placed in a friction mill that operated at 1025 rpm at room temperature without friction. After 2 hours the mill was heated to 51 ° C and there was 95% de-stratification and demetalization.

EXAMPLE 6

A suspension of compact discs in 60% scales (2220 g) and a 40% solution of 15% acetic acid (1258 g of water / 222 g of acetic acid) were placed in a friction mill operating at 1025 rpm at room temperature without friction. After 2 hours the mill was heated to 49 ° C and there was 100% de-stratification and demetalization

EXAMPLE 7

A suspension of compact discs in 60% scales (150 g) and a 40% solution of 1% acetic acid (10 kg) were placed in a 250 liter high speed industrial dispersion mixer operating at 1350 rpm at room temperature. After 2.75 hours the mill was heated to 93 ° C and there was 100% de-stratification.

EXAMPLE 8

A suspension of compact discs in 53% scales (125 kg) and a 47% solution of acetic acid (110 kg) were placed in a 250 liter high speed industrial dispersion mixer that initially operated at 800 rpm to facilitate "Wetting" of the scale. The liquids were introduced at 60 ° C. After approximately 10 minutes, the scale was wetted and the mixer speed increased to 1350 rpm. After 3 hours, the mill was heated to 90 ° C and there was major de-stratification and demetalization (70-80%).

EXAMPLE 9

A suspension of compact discs in 12% scales (5 kg), a solution of digital video discs in 48% scales and a 40% solution of 1% acetic acid (17 kg) were placed in an industrial dispersion mixer of 50-liter high speed running at 1600 rpm. The liquids were introduced at 60 ° C. The temperature rose to 94 ° C after 30 minutes. Complete demetalization was observed in less than 90 minutes.

EXAMPLE 10

A suspension of compact discs in 60% flakes (127 kg) and a 40% solution of 1% acetic acid (84.5 kg) were placed in a 250 liter high speed industrial dispersion mixer that operated between 1350 rpm and 1600 rpm. After about 4 hours the temperature had risen to 92 ° C. Initially, more solution was added to improve fluidity and promote mixing of the suspension (reducing the total solids content up to about 45%). After the temperature had reached 60 ° C, this additional fluid was drained. The scale was almost completely demetallized after 4 hours, with residual metal remaining on the larger scales and 100% demetalization and de-stratification evident on the smaller scales.

EXAMPLE 11

A suspension of digital video discs in 60% scales (26 kg) and 40% water (17 kg) was placed in a high-speed 50 liter dispersion mixer at room temperature, operating at 2000 rpm. After 5 hours, the batch temperature had risen to 98 ° C with partial demetallization and de-stratification (80-90%) evident as a whole. Residual metal remained on the larger scales, with 100% demetalization and de-stratification evident on the smaller scales

Claims (23)

1. A method for removing a coating from a polymeric substrate having a coating thereon, said process comprising the steps of:

(to)

 fragment said polymeric substrate into smaller polymeric particles;

(b)

 providing said polymeric substrate particles to a mechanical shear apparatus;

(C)

 fluidize said polymeric substrate particles in a fluidization medium;

(d)

subjecting said fluidized particles to said mechanical shear apparatus equipped with a mixing blade at a relatively high shear rate equivalent to a blade speed of more than 800 ppm and a circumferential speed of the blade of at least 10 m / s to remove the coating of the polymeric substrate; Y

(and)

 recovering the cleaned polymer particles, in which the fluidization medium comprises water, is free of caustic agents and the solids content in the fluidization medium ranges from 50 to 60 percent by weight.

2.

 The process according to claim 1, wherein said polymeric substrate comprises a polycarbonate.

3.

 The method according to claim 2, wherein said polymeric substrate comprises an optical medium.

Four.

 The method according to claim 1, wherein said polymeric substrate is derived from optical means comprising a compact disc, a digital video disc or mixtures thereof.

5.

 The method according to claim 1, wherein said polymeric substrate particles comprise particles ranging in size from 2 to 20 millimeters in the longest direction.

6.

 The process according to claim 1, wherein an accelerator selected from the group consisting of carboxylic acids, carboxylic acid esters and mixtures thereof is additionally added to said shear process.

7.

 The process according to claim 6, wherein said accelerator comprises aqueous acetic acid.

8.

 The process according to claim 7, wherein the concentration of acetic acid ranges from 0.1% to 20% by weight based on the weight of the aqueous acetic acid.

9.

 The process according to claim 8, wherein the concentration of acetic acid ranges from 0.1% to 10% by weight.

10.

 The process according to claim 9, wherein the concentration of acetic acid ranges from 0.25 to 1 percent by weight.

eleven.

 The method according to claim 6, wherein said accelerator comprises a lactate.

12.

 The process according to claim 1, wherein the shear temperature is less than 95 ° C.

13.

 The process according to claim 12, wherein the shear temperature ranges from 50 to 95 ° C.

14.

 The method according to claim 1, wherein said shear apparatus comprises a rotating blade mixer operating at a mixing speed of at least 1000 rpm.

fifteen.

 The method according to claim 1, wherein step (d) comprises washing said polymeric particles subjected to shear.

16.

 The method according to claim 15, wherein said washing step comprises washing with water.

17.

 The process according to claim 16, wherein said washing step comprises washing with water in the presence of an organic acid, a surfactant or a mixture thereof.

18.

 The process according to claim 3, further comprising the step of recovering aluminum from the mixing effluent.

The method according to claim 4, further comprising the step of recovering gold from the mixing effluent. 20. A method for demetalizing and removing a coating from a polymeric substrate having a metal-containing coating thereon, said process comprising the steps of: (a) fragmenting said polymeric substrate into smaller polymeric substrate particles; 10 (b) providing said polymeric substrate particles to a mechanical shear apparatus;

(C)

 fluidize said polymeric substrate particles in a fluidization medium;

(d)

 subjecting said fluidized particles in said mechanical shear apparatus to shear at a relatively high shear rate equivalent to a blade speed of more than 800 ppm and a circumferential blade speed of at least 10 m / s to remove the coating of the polymeric substrate in

Presence of an accelerator selected from the group consisting of a carboxylic acid, a carboxylic acid ester and mixtures thereof; Y (e) recover the cleaned polymer particles. 21. The method according to claim 20, wherein said fluidizing means comprises water. 22. The method according to claim 1 or 20, wherein the shear rate is defined by a circumferential speed of the blade of at least 18 m / s.

2. 3.

 The method according to claim 1 or 20, wherein the shear rate is defined by a blade speed of at least 1000 rpm and a circumferential blade speed of at least 18 m / s.

24.

The process according to claim 1, wherein the fluidization medium comprises an organic acid as an accelerator.